How do I prevent the brush color using a gradient in the weights?
So from what I see, since 2.8, there's a difference in the way the weight painting gradient is displayed. In 2.79, if you have a vertex that has a weight of 1 and the next one that has a weight of 0, there will be a red to blue gradient (here with a simple non-subdivided cube):

Since 2.8 you have a red to blue gradient but with all the yellow and green nuances. But it doesn't change anything, the weight of the vertex on the left is still 1 and the weight of the vertex on the right is still 0: